Journal
SURFACE SCIENCE
Volume 606, Issue 3-4, Pages 554-558Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.susc.2011.11.029
Keywords
Strontium titanate; Surface preparation; X-ray photoemission
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Funding
- U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [10122]
- Department of Energy's Office of Biological and Environmental Research at Pacific Northwest National Laboratory
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We show that the HF acid etch commonly used to prepare SrTiO3(001) for heteroepitaxial growth of complex oxides results in a non-negligible level of F doping within the terminal surface layer of TiO2. Using a combination of x-ray photoelectron spectroscopy and scanned angle x-ray photoelectron diffraction, we determine that on average similar to 13% of the O anions in the surface layer are replaced by F. but that F does not occupy O sites in deeper layers. Despite this perturbation to the surface, the Fermi level remains unpinned, and the surface-state density, which determines the amount of band bending, is driven by factors other than F doping. The presence of F at the STO surface is expected to result in lower electron mobilities at complex oxide hetero-junctions involving STO substrates because of impurity scattering. Unintentional F doping can be substantially reduced by replacing the HF-etch step with a boil in deionized water, which in conjunction with an oxygen tube furnace anneal, leaves the surface flat and TiO2 terminated. (C) 2011 Elsevier B.V. All rights reserved.
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